Gsellman, who batted for himself in the 12th, was hit by a pitch by Atlanta reliever Josh Ravin. He advanced to second on a sacrifice bunt and scored on a single by Yoenis Cespedes. Gsellman slid in ahead of the throw from right fielder Nick Markakis.
The Mets added an insurance run when Asdrubel Cabrera doubled to right to drive in Cespedes.
New York closer Jeurys Familia pitched a scoreless 12th, giving him 11 1/3 consecutive scoreless innings, to earn his eighth save.
Gsellman (2-0) allowed one hit and one walk in two innings, with three strikeouts.
Ravin (0-1) worked two innings and allowed two runs on two hits and one walk, with one strikeout. Ravin had been activated on Friday when the Braves sent Lucas Sims to Triple-A Gwinnett. Ravin had missed 17 games with a viral infection.
New York (14-5) is now 2-0 in extra inning games. Atlanta (11-8) is 1-4 in extra innings.
Both starting pitchers were effective on Friday, but neither figured in the decision.
New York's Noah Syndergaard allowed three runs in six innings. He allowed seven hits, one a home run, and struck out six.
Atlanta's Sean Newcomb also pitched six innings and allowed three runs (two earned) on six hits and three walks. He struck out five.
The Braves got on the board in the first inning when Ozzie Albies hit a solo homer, his sixth
The Mets took a 2-1 lead in the third inning. Amed Rosario doubled home Tomas Nido and took third on a throwing error by center fielder Ender Inciarte. Rosario scored on Michael Conforto's sacrifice fly to left field.
New York added a run in the fourth when Wilmer Flores singled in Todd Frazier to make it 3-1.
Atlanta closed the gap to 3-2 in the fourth when Dansby Swanson scored on Ryan Flaherty's double to right field.
The Braves tied it in the sixth when Kurt Suzuki drove home Nick Markakis with a sacrifice fly. Markakis led off the inning with a double and reached third on a wild pitch.
The third game of the four-game series will be played on Saturday. New York will send right-hander Jacob deGrom (2-0, 3.24) against Atlanta right-hander Julio Teheran (1-1, 5.40).
--Field Level Media
NY Mets | Atlanta | |
Noah Syndergaard | Player | Sean Newcomb |
No Decision | W/L | No Decision |
6.0 | IP | 6.0 |
6 | Strikeouts | 5 |
7 | Hits | 6 |
4.50 | ERA | 3.00 |
NY Mets | Atlanta | |
Amed Rosario | Player | Ryan Flaherty |
2 | Hits | 2 |
1 | RBI | 1 |
0 | HR | 0 |
4 | TB | 3 |
.500 | Avg | .500 |